1. Field of the Invention
The present invention relates to a navigation system and a program thereof, which calculates a total cost (a total profile value) for each of plurality of possible routes to a destination and determines a recommended route such that the recommended route has the smallest cost among the possible routes. The navigation system and the program thereof also guide a driver of a vehicle to the recommended route. The present invention also relates to a navigation system and a program thereof for guiding a vehicle to recommended lanes on a road (i.e., lane navigation).
2. Description of Related Art
Conventionally, a navigation system, which calculates a total cost (a total profile value) for each of plurality of possible routes to a destination and determines a recommended route such that the recommended route has the smallest cost among the possible routes, has been proposed. The navigation system also guides a vehicle to the recommended route. The navigation system calculates the total cost of each of possible routes by summing a cost part of each link corresponding to a road section located on the route. The cost part of each link in the route depends on various factors, such as a length, a width and a type of the corresponding road section of the link. Also, the cost part of each link varies when the corresponding road section of the link is located immediately after another road section in the route, which turns in a right or left direction. For example, the cost of one route becomes higher at the time a traffic jam occurs on a road corresponding to a certain link of the route than at the time the traffic jam does not occur.
However, the above-described conventional navigation system has the following disadvantages. FIG. 1 is a top view showing a road configuration, which includes a highway main road 41. The road configuration includes the highway main road 41, an entrance road (an entrance ramp) 42, an exit road (an exit ramp) 43, an exit road (an exit ramp) 44, a road 45. The highway main road 41 includes two lanes going one way. The entrance road 42 merges with the highway main road 41 at a merge point on a right side thereof. The exit road 43 branches from the highway main road 41 on the right side thereof at an upstream side of the merge point, where the entrance road 42 merges into the highway main road 41. The exit road 44 branches from the highway main road 41 on the right side thereof at a branch point located on a downstream side of the merge point. The exit road 43 and the exit road 44 merge together to form the road 45.
Under the above-described road configuration, we discuss the navigation system to calculate a recommended route to a facility located on a downstream side of the road 45 for a vehicle, which drives in a right direction on the highway main road 41 coming from a left end in FIG. 1. Usually, the navigation system calculates the cost in such a manner that the cost of one route that travels along a branch road, such as an exit road, becomes larger than the cost of the other route that travels along a main road. As a result, the navigator system determines a route 46, which travels along the highway main road 41, as the recommended route because of its small cost. As a result, a route 47, which travels along the exit road 43, is not determined as the recommended route.
The route 46 on the highway main road 41 is led to the exit road 44 from one side of the highway main road 41 after the entrance road 42 is merged into the highway main road 41 on the common side thereof. Therefore, in some cases, a vehicle that drives on the highway main road 41 may suffer from crossing another vehicle path that approaches the highway main road 41 through a route 60 shown by an arrow. As a result, in the case, where a distance between a branch point 49 and a merge point 50 is shorter, a driver of the vehicle on the main road does not calmly deal with the other vehicle that cuts in the main road 41. Therefore, psychological stress for the driver becomes larger. Here, the branch point 49 is located at a point where the exit road 44 branches from the highway main road 41. The merge point 50 is located at a point where the entrance road 42 is merged into the highway main road 41. As a result, a driving along the route 47 to the destination may be more preferable than a driving along the route 46 in some cases.
Also, in a case where the exit road 43 did not exist, a driving along a route 48, which travels along the highway main road 41, might be more preferable when the risk of a collision with the other vehicle at the merge point 50 is taken into consideration. When driving along the route 48, the vehicle passes by the branch point 49 and drives along the highway main road 41 in order to exit the main road 41 through another safe exit road located on a downstream side of the branch point 49.
The present invention also relates to a navigation system and a program thereof for guiding a vehicle to recommended lanes on a road (i.e., lane navigation).
Conventionally, Japanese Unexamined Patent Publication No. 2000-266556 corresponding to U.S. Pat. No. 6,466,867 and Japanese Unexamined Patent Publication No. 2000-18956 have disclosed navigation systems, which guide a recommended lane by use of an enlarged map and a voice for a navigation point, when a road to the navigation point has multiple lanes. The navigation systems may guide the recommended lane by voices, which go like “turn right at X meters ahead, so change the lane to the right lane”. Here, the navigation point includes an intersection along a recommended route to a destination.
However, for example, after this lane navigation is performed, the vehicle may have difficulties in changing lanes to the recommended lane to follow the recommended route, when the vehicle is going to enter the navigation point, which is a target of the lane navigation. This is because the vehicle may be still driving on a lane located away from the recommended lane that the lane navigation recommends, and also because the recommended lane may be filled with other vehicles. It is desirable to avoid changing lanes at such an unreasonable state, when a safety of the vehicle is taken into consideration.